Such a drive is known from public prior use. Components, such as for example vertically adjustable head restraints of vehicle seats, are equipped with an electric motor that moves the head part of the head restraint for example up or down relative to a seat back. The drive motor is regulated by a controller, for example the seat controller, according to the required displacement path and the required displacement direction.
In this case the seat controller uses a signal of the drive motor that is provided to it with a pulse rate corresponding to the speed of the drive motor. For this purpose the drive motor has a sensor that records the motor speed and converts it into a pulse rate corresponding to the motor speed. This may for example be a Hall effect sensor.
The design of the component requires that the drive motor be small and/or of low weight and/or have a low noise level and/or low noise levels. The noise level of the drive motor is influenced for example by the load acting on the drive motor. The load depends for example on the displacement direction. For example, different loads act on the drive motor as a function of whether the component is displaced upward against gravity or downward in the direction of gravity. If for example a head restraint is displaced against gravity, the load on the drive motor is greater. This generally leads to a different noise level than in the case of a displacement movement of the head restraint downward in the direction of gravity.
Also, higher loads caused by a greater coefficient of friction in the guides of the component or by lower temperatures lead to a higher noise level of the drive motor. If the conditions change over the displacement range, fluctuations of the noise level can occur during operation of the drive motor.
In this case, with regard to the running noise, load fluctuations have a greater effect at high operating speeds than at low operating speeds.
In order to meet the requirements for low weight and small overall size of the component, small drive motors are used. However, these must be operated at high motor speeds. However, load fluctuations then lead to greater noise fluctuations in comparison with drive motors with a low operating speed.
The necessary motor power depends upon the maximum load possible in the system. This motor power results from the actual coefficients of friction of the guides, the effect of the mass of the head restraint and the effect of temperature changes.
In the case of small drive motors this power is generally generated with high motor speeds, so that in the event of variably occurring loads the operating speed is sometimes in a range at which the pulse rate of commercially available controllers transmitted by a sensor can no longer be processed and can lead to malfunction of the controller or of the drive system.